Galvanic process for filling through-holes with metals, in particular of printed circuit boards with copper

ABSTRACT

The present invention relates to a galvanic process for filling through-holes with metals. The process is particularly suitable for filling through-holes of printed circuit boards with copper.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.11/661,704, filed on 22 Dec. 2008, now U.S. Pat. No. 9,445,510 B2, whichis a U.S. National Stage Application based on and claiming benefit andpriority under 35 U.S.C. §371 of International Application No.PCT/EP2005/009332, filed 30 Aug. 2005, which in turn claims benefit ofand priority to German Application No. 10 2004 045 451.5 filed 20 Sep.2004, the entirety of each of which is hereby incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a galvanic process for fillingthrough-holes with metals. The process is particularly suitable forfilling through-holes of printed circuit boards with copper. The processprovides durable fillings even in the case of small hole diameters,undesired inclusions in the through-hole can be avoided. Furthermore,the filling exhibits very good thermal conductivity.

BACKGROUND

The ever increasing miniaturization of electronic componentssimultaneously leads to an increase in the integration density. Inprinted circuit boards the trend towards miniaturization is reflected inthe following construction parameters: reduction of pad diameters andconductor width/conductor gap as well as improved registration andincrease in the number of layers (cf. Der europäische Technologie- undTrendbericht 2001/2002 Ober Leiterplatten mit hohen Integrationsdichten¹). ¹The European Technology and Tred Report 2001/2002 ConcerningPrinted Circuit Boards with High Integration densities

Printed circuit boards having these properties are generally referred toas printed circuit boards with high integration density (so-called HighDensity Interconnection or HDI).

An important aspect in such HDI circuits in printed circuit boardproduction is the filling of through-holes (so-called via-holes). Thefilling of the through-holes puts extremely high requirements on processcontrol. The most different types of drill holes have to be taken intoaccount, the various requirements on the filler materials have to be metand the subsequent working steps in a printed circuit board have to betaken into account.

The main focus of the present invention is the filling of through-holesin printed circuit boards which go through the entire board (PlatedThrough Hole, PTH) and of interior vias (buried vias).

In principle, the process is suitable for filling through-holes in themost different workpieces, in particular board-shaped workpieces andboard-shaped electric circuit carriers containing through-holes.

The closing of the through-holes is necessary inter alia so as toprevent the deposition of solder on the components, to achieve a highintegration density and to improve the electrical properties. Inmulti-layer printed circuit boards inclusions (of air, solvent, etc.) inthe holes might occur during the laminating of the next build-up layer,which inclusions later on in the case of thermal stresses lead to bulgesand, consequently, cracks in the next layer.

Thus, the main requirements to be fulfilled by the filler materials forthrough-holes are:

-   -   the absence of solvents    -   good adhesive properties to the sleeve and solder resist    -   resistance to process chemicals in subsequent steps (e.g.        galvanic metallization with nickel, gold or tin).    -   resistance in hot air leveling processes.

In the state of the art various processes for filling through-holes aredescribed.

In the simplest case the holes are filled using a specially adjustedsolder resist. They have the advantage to offer that in the case of highintegration density no impairment is caused in the resolution by the viafiller which necessarily protrudes like a rivet head. However, what isdisadvantageous is the danger of solvent inclusions which can abruptlyevaporate in subsequent process steps, such as tinning, and, thus, tearopen the cover.

However, this process is not suitable for closing through-holes in innerlayers. Here, the inner layers have to be completely closed in order toavoid inclusions. For this process plugging is widely used because bymeans of this process it is possible by means of copper-plating thefilled through-holes to create an inner layer which can be structuredwithout any limitations.

As filler material various dielectrics such as resin-coated copper foils(RCC) or photo-dielectric liquid or dry films are used.

EP 0 645 950 B1 describes a process for producing multi-layered circuitsubstrates. As filler material for through-holes thermosetting resinsare used chosen from the group consisting of phenolic resin and epoxyresin. Furthermore, as a conductive substance at least one metal powderchosen from the group consisting of silver, nickel, copper and an alloythereof is added to the resin.

As a rule, the plugging is done after the printed circuit board has beendrilled and the drill holes finally metallized, however, before thestructuring. After the vias have been filled and the plugging paste hasbeen cured, the latter is mechanically leveled since due to the fillingprocess it exhibits a slight rivet head. Often, a metallization of thepaste with copper is subsequently carried out so that a continuouscopper layer is created as final layer. To put it simply, the followingsteps are required:

-   -   drilling    -   metallizing the sleeve    -   plugging    -   brushing, grinding    -   metallizing the plugging paste    -   applying the next build-up layer.

EP 1 194 023 A1 describes the manufacturing of HDI printed circuitboards by filling through-holes with conductive pastes, wherein thecuring of the paste can occur at the same time as the molding of thebasic material so that an electric contact of interior layers results.

However, the processes involve much outlay and cause a great deal of theprocess costs in the manufacture of HDI printed circuit boards.Furthermore, for each layout on the printed circuit board a differentprinting mask has to be used. Therefore, the process cannot beuniversally used.

In the case of highly different drill hole diameters on the printedcircuit board the printing process is difficult.

SUMMARY

Therefore, it is the object of the present invention to develop aprocess which avoids the disadvantages mentioned and provides a simpleprocess for reliably filling the through-holes of a workpiece withnearly no inclusions. The process can be used in particular for fillingthe through-holes in printed-circuit boards with copper.

A further object of the invention is to achieve a high performance inthe electrolytic metallization. In the present case, this means that, onthe one hand, the current density during the electrolytic metallizationof a printed circuit board has to be as high as possible in order toachieve a short working time and, on the other hand, that the amount ofmetal deposited on the surface of a printed circuit board is to be assmall as possible.

The object is achieved by using the inventive process for fillingthrough-holes of a workpiece with metals comprising the followingprocess steps:

-   -   (i) Bringing in contact the workpiece containing through-holes        with a metal-deposition electrolyte and applying a voltage        between the workpiece and at least one anode so that a current        flow is supplied to the workpiece, wherein the current flow is        chosen such that in accordance with FIG. 1 a preferred        deposition occurs in the center of the through-holes and,        consequently, the through-holes completely or almost completely        grow together;    -   (ii) Further bringing in contact the workpiece with a        metal-deposition electrolyte and applying a voltage between the        workpiece and at least one anode so that a current flow is        supplied to the workpiece, wherein the through-holes obtained in        step (i) which are completely or almost completely divided into        to halves are filled by the metal up to the desired degree in        accordance with FIG. 2.

By using the inventive two-step process it becomes possible for thefirst time to fill a through-hole with a pure metal layer, in contrastto the state-of-the-art processes for filling which use pastes—mostlyconductive—since up to now it has been assumed that the production of acompact metal layer is not possible with the required durability and thedesired properties.

In the conventional metallization of holes, for example in printedcircuit boards, at first an almost identical scattering can be observedat the ends of the holes as well as in their center. During themetal-deposition the aspects ratio changes and the scattering decreasesin the drill hole. This leads to increased metal-deposition at the endsof the drill holes which grow together before the interior is fillinglymetallized. Thus, undesired inclusions are left in the holes, inparticular remainders of the metallization bath.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are described herein withreference to the drawings, in which:

FIG. 1a is a diagram depicting a V-shaped deposit located m athrough-hole of a workpiece;

FIG. 1b is a diagram depicting a rounded narrow shaped deposit locatedin a through-hole of a workpiece;

FIG. 2 is a diagram depicting a through-hole of a workpiece afterformation of a narrow part in the hole center and subsequent filling ofthe through-hole; and

FIG. 3 is a diagram depicting a pulse reverse current with a phase-shiftand a pulse pause.

DETAILED DESCRIPTION

The present invention is based on the idea to create in the first stepof a special deposition technique two holes from the through-hole bycompletely or almost completely filling the hole center, which two holesare each closed at one end close to the hole center (cf. FIG. 1). Theshape of the deposit in the area of the through-hole center can beV-shaped, as is shown in FIG. 1a , or it can be in the shape of arounded narrow part (cf. FIG. 1b ). This shape of the deposit can beachieved by increased scattering in the area of the through-hole centerso that here an increased deposition of metal compared to the ends ofthe through-hole can be observed.

In printed circuit board production, a preferred field of application ofthe present invention, these holes are also referred to as blind holesor blind vias. In a second metallization step the thus created blindvias are then filled with metal (cf. FIG. 2).

Processes for filling blind vias are actually known and described in thestate of the art.

EP 1 264 918 A1 describes an electrolytic copper deposition processwhich is particularly suitable for filing micro blind vias. Here, theuse of inert anodes in a dummy plating phase helps to maintain andimprove the fillability of the electrolyte.

According to EP 1 219 729 A1 chemical substances such as formaldehydebut also oxidizing agents are used in order to lengthen the period ofstability of the metallization bath, which is particularly suitable forfilling micro blind vias. As additives sulfur-containing substances withsulfonic acid groups as well as thiol-reactive compounds are used.

DE 103 25 101 describes a process for filling micro blind viascharacterized by the following steps:

-   -   (i) Using a bath electrolyte for galvanic plating with metallic        coatings comprising metals salts, acids and organic additives,        wherein the bath contains an inorganic matrix comprising 15-60        g/l copper, 40-300 g/l sulfuric acid and 20-150 mg/l chloride        and the organic additives comprise brightening agents, wetting        agents and further additives chosen from polyamides, polyamines,        lactam alkoxylates, thiourea, oligomeric and polymeric        phenazonium derivatives and amino-triphenylmethane dyes,    -   (ii) operating the bath with a direct current at a density of        0.5-2.5 A/dm², or current pulses at an effective current density        of 0.5-10 A/dm²,    -   (iii) withdrawing part of the electrolyte from the galvanic        bath,    -   (iv) adding an oxidizing agent to the part which has been        withdrawn,    -   (v) optionally irradiating the withdrawn electrolyte with UV        light and    -   (vi) recycling the withdrawn part to the galvanic bath and        supplementing the organic additives destroyed by the oxidation        treatment.

In a preferred embodiment of the present invention the process servesfor filing the through-holes in printed circuit boards with a maximumheight of 3.5 mm, a preferred height of 0.025-1 mm and a particularlypreferred height of 0.05-0.5 mm as well as a diameter of 1000 μm atmost, preferably 30-300 μm and most preferably 60-150 μm.

In the inventive process for filling through-holes of a workpiece withmetals, in principle, every electrolyte suitable for galvanicmetal-deposition can be used, such as electrolytes for depositing gold,tin, nickel or alloys thereof. The preferred metal is copper.

It has been shown that for copper-deposition electrolytes having thecomposition described in the following provide the best results:

Copper can be given into the electrolyte as copper sulfate pentahydrate(CuSO_(4×)5H2O) or as copper sulfate solution. The working range isbetween 15-75 g/l copper.

Sulfuric acid (H₂SO₄) is added as 50-96% solution. The working range isbetween 20-400 g/l, preferably 50-300 g/l.

Chloride is added as sodium chloride (NaCl) or as hydrochloric acidsolution (HCl). Here, the working range of chloride is between 20-200mg/l, preferably 30-60 mg/l.

Furthermore, the electrolyte preferably comprises brightening agents,leveling agents and wetting agents as organic additives.

Usually, wetting agents are oxygen-containing, high-molecular compoundsin concentrations of 0.005-20 g/l, preferably 0.01-5 g/l. Examples aregiven in

TABLE 1 Wetting agent Carboxymethylcellulose NonylphenolpolyglycoletherOctanediol-bis-(polyalkylene glycol ether) Octanol polyalkylene glycolether Oleic acid polyglycol ester Polyethylene glycolpolypropyleneglycol copolymerisate Polyethylene glycol Polyethylene glycoldimethylether Polypropylene glycol Polyvinylalcohol β-naphthylpolyglycolether Stearic acid polyglycol ester Stearic acid alcoholpolyglycolether

In general, as brightening agents sulfur-containing substances are usedwhich are listed in Table 2:

TABLE 2 Sulfur compounds 3-(Benzothiazolyl-2-thio)-propyl sulfonic acid,sodium salt 3-Mercaptopropane-1-sulfonic acid, sodium salt Ethylenedithiodipropyl sulfonic acid, sodium salt Bis-(p-sulfophenyl)-disulfide,disodium salt Bis-(ω-sulfobutyl)-disulfide, disodium saltBis-(ω-sulfohydroxypropyl)-disulfide, disodium saltBis-(ω-sulfopropyl)-disulfide, disodium saltBis-(ω-sulfopropyl)-sulfide, disodium saltMethyl-(ω-sulfopropyl)-disulfide, disodium saltMethyl-(ω-sulfopropyl)-trisulfide, disodium salt O-ethyldithio-carbonicacid-S-(ω-sulfopropyl)-ester, potassium salt Thioglycolic acidThiophosphoric acid-O-ethyl-bis-(ω-sulfopropyl)-ester, disodium saltThiophosphoric acid-(ω-sulfopropyl)-ester, trisodium salt

As leveling agents polymeric nitrogen compounds (e.g. polyamines orpolyamides) or nitrogen-containing sulfur compounds, such as thioureaderivatives or lactam alkoxylate, as described in DE 38 36 521 C2 can beused. The concentrations of the substances used are in a range from0.1-100 ppm.

Furthermore, also polymeric phenazonium derivatives, which are describedin the patent DE 41 26 502 C1, can be used. Further substances which areused for filling blind vias are coloring agents on the basis of anaminotriphenylmethane structure such as malachite, rosalinine or crystalviolet.

As anodes for example inert anodes without and with redox system (i.e.with Fe^(2+/3+) system, for example) can be used. When using an ironredox system the concentration of iron(II) ions is 1-15 g/l in general,preferably 8-12 g/l, and the concentration of iron(III) ions is 1-15 g/lin general and preferably 8-12 g/l.

For acidic copper, DC and AC electrolytes also soluble anodes can beused.

During the metallization with copper the metal is deposited not only inthe through-holes but also on the surface of the substrate. If desired,the copper layer on the surface can be removed again using the etchingprocesses known in printed circuit board production. To this end, forexample solutions containing iron(III) chloride are suitable.

Furthermore, it has been observed that the filling with metals achievesparticularly good results in horizontal processes using a special typeof metallization by means of a pulse reverse current. This specialtechnique is characterized by a 180° phase shift between the two pulseforms which are generated by two separate pulse rectifiers. By means ofthe two rectifiers the two sides of a printed circuit board can beindividually metallized. A further characteristic consists in the use ofa periodically repeating pulse pause for both rectifiers which is chosensuch that at the same time the reverse current pulse acts on the otherside, cf. FIG. 3.

Reverse pulse plating was developed for the electrolytic deposition ofcopper in particular on printed circuit boards with a high aspect ratioand is described in DE 42 25 961 C2 and DE 27 39 427 A1, for example. Byusing high current densities an improved surface distribution andscattering in the through-holes is achieved.

In the inventive process the following parameters are preferablyadjusted:

The ratio of the duration of the at least one forward current pulse tothe duration of the at least one reverse current pulse is adjusted to atleast 5, preferably to at least 15 and more preferably to at least 18.This ratio can be adjusted to 75 at most and preferably to 50 at most.It is particularly preferred to adjust this ratio to about 20.

The duration of the at least one forward current pulse can be adjustedto preferably at least 5 ms to 250 ms.

The duration of the at least one reverse current pulse is preferablyadjusted to 20 ms at most and most preferably to 1-10 ms.

The peak current density of the at least one forward current pulse atthe workpiece is preferably adjusted to a value of 15 A/dm² at most.Particularly preferable is a peak current density of the at least oneforward current pulse at the workpiece of about 1.5-8 A/dm² inhorizontal processes. In vertical processes the most preferred peakcurrent density of the at least one forward current pulse at theworkpiece is 2 A/dm² at most.

The peak current density of the at least one reverse current pulse atthe work piece will preferably be adjusted to a value of 60 A/dm² atmost. Particularly preferred is a peak current density of the at leastone reverse current pulse at the workpiece of about 30-50 A/dm² inhorizontal processes. In vertical processes the most preferred peakcurrent density of the at least one reverse current pulse at theworkpiece is 3-10 A/dm² at most.

In a preferred embodiment of the present invention the process comprisesthe following steps:

-   -   a. a first voltage is applied between a first side of the        workpiece and at least a first anode so that a first pulse        reverse current is supplied to the first side of the workpiece,        wherein in every cycle of this first pulse reverse current at        least a first forward current pulse and at least a first reverse        current pulse flow.    -   b. a second voltage is applied between a second side of the        workpiece and at least a second anode so that a second pulse        reverse current is supplied to the second side of the workpiece,        wherein in every cycle of this second pulse reverse current at        least a second forward current pulse and at least a second        reverse current pulse flow.

As regards the latter embodiment the at least one first forward currentpulse and the at least one first reverse current pulse, respectively,can be offset relative to the at least one second forward current pulseand to the at least one second reverse current pulse, respectively. In afurther preferred embodiment of the present invention this offsetbetween the first and second current pulses amounts to about 180°.

In order to further improve the scattering the current flow in everycycle can comprise two forward current pulses, wherein between the twoforward current pulses and a reverse current pulse a zero currentinterruption is provided.

In the further progress of the metallization process at least oneparameter of the pulse reverse current can be varied, wherein thisparameter is chosen from a group comprising the ratio of the duration ofthe forward current pulse to the duration of the reverse current pulseand the ratio of the peak current density of the forward current pulseto the peak current density of the reverse current pulse. It has beenproven to be particularly advantageous to increase the ratio of the peakcurrent density of the forward current pulse to the peak current densityof the reverse current pulse when metallizing the workpiece and/or todecrease the ratio of the duration of the forward current pulse to theduration of the reverse current pulse.

The invention is further explained by means of the following examples:

Horizontal Metallization Process

The Inpulse® 2 modules of Atotech Deutschland GmbH used for horizontaltreatment of printed circuit boards (in which boards for treatment aretransported horizontally and in a horizontal transportation plane) havea gap of 15 mm between the nozzle holder and the cathode (workpiece) anda gap of 8 mm between anode and cathode.

For the metallization a printed circuit board of FR4 material is usedhaving the dimensions 18′×24″=457 mm×610 mm and a through-hole diameterof 150 μm and a height of 200 μm, unless stated otherwise.

Prior to metallization the surface of the printed circuit board is firstof all cleansed for 45 seconds with the cleaner Cuprapro™ CF of AtotechDeutschland GmbH and then treated for 45 seconds with 5% sulfuric acid.

The electrolytes used have the following composition. The concentrationof the copper ions and the sulfuric acid is individually given in thetests. In all cases, the metallization is carried out at a temperatureof 40° C.

-   -   copper sulfate    -   sulfuric acid    -   chloride ions: 50 mg/l    -   iron(II): 10 g/l    -   iron(III): 2 g/l    -   leveling agent Inpulse® H6: 4 ml/l; brightening agent Inpulse®        H6: 7 ml/l    -   leveling agent Inpulse® HF: 4 ml/l; brightening agent Inpulse®        HF: 7 ml/l    -   Inpulse™ leveling agent and brightening agent are products of        Atotech Deutschland GmbH.

EXAMPLE 1

According to the above-described general execution rule for horizontalprocesses the printed circuit board is at first treated for 30 minutesin a bath for electrolytic metallization with copper with the Inpulse®H6 process and a pulse reverse current process with the parametersaccording to Table 1a. A copper deposition in the through-holes as isshown in FIG. 1a is obtained.

Then, the printed circuit board is treated for a further 30 minutes in asecond bath for electrolytic metallization with copper with the Inpulse®HF process and a pulse reverse current process with the parametersaccording to Table 1b. A copper deposition in the through-holes as isshown in FIG. 2 is obtained.

Then, the filling of the through-holes is complete. No inclusions areobserved.

TABLE 1a pulse parameters in the metallization with copper I_(forward)/pulse parameter pulse phase sulfuric I_(reverse) in ms forward/ pauseshift copper acid test in A/dm² reverse pulse in ms in ° g/l g/l 1a 6/40108/6 6 180 40 200 1b 6/40  72/4 4 180 60 150

EXAMPLE 2

According to the above-described general execution rule for horizontalprocesses the printed circuit board is at first treated for 30 minutesin a bath for electrolytic metallization with copper with the Inpulse®H6 process and a pulse reverse current process with the parametersaccording to Table 2a.

Then, the printed circuit board is treated for a further 30 minutes in asecond bath for electrolytic metallization with copper with the Inpulse®HF process and a pulse reverse current process with the parametersaccording to Table 2b.

Then, the filling of the through-holes is complete. No inclusions areobserved.

TABLE 2a pulse parameters in the metallization with copper I_(forward)/pulse parameter pulse phase sulfuric I_(reverse) in ms forward/ pauseshift copper acid test in A/dm² reverse pulse in ms in ° g/l g/l 2a 6/40216/12 12 180 40 200 2b 6/40 72/4 4 180 60 150

EXAMPLE 3

According to the above-described general execution rule for horizontalprocesses the printed circuit board is treated for 60 minutes in a bathfor electrolytic metallization with copper with the Inpulse® HF processand a pulse reverse current process with the parameters according toTable 3.

Then, the filling of the through-holes is complete. No inclusions areobserved.

TABLE 3 pulse parameters in the metallization with copper I_(forward)/pulse parameter pulse phase sulfuric I_(reverse) in ms forward/ pauseshift copper acid test in A/dm² reverse pulse in ms in ° g/l g/l 3 6/4072/4 4 180 60 150

EXAMPLE 4

According to the above-described general execution rule for horizontalprocesses a printed circuit board having a through-hole diameter of 200μm and a height of 300 μm is at first treated for 30 minutes in a bathfor electrolytic metallization with copper with the Inpulse® H6 processand a pulse reverse current process with the parameters according toTable 4a.

Then, the printed circuit board is treated for a further 30 minutes in asecond bath for electrolytic metallization with copper with the Inpulse®HF process and a pulse reverse current process with the parametersaccording to Table 4b.

Then, the filling of the through-holes is complete. No inclusions areobserved.

TABLE 4 pulse parameters in the metallization with copper I_(forward)/pulse parameter pulse phase sulfuric I_(reverse) in ms forward/ pauseshift copper acid test in A/dm² reverse pulse in ms in ° g/l g/l 4a 6/40108/6 6 180 40 200 4b 6/40  72/4 4 180 60 150

In all tests a pulse pause and a 180° phase shift at the pulse parameterwere adjusted. This means that the reverse pulse was applied to theanodes at one side of the test board and that, at the same time, thepulse pause was applied to the anodes of the other side. The schematicrepresentation of the pulse form in FIG. 3 (current as function of thetime) shows the adjustment with a phase shift between the upper and thelower anodes (upper curve: current at the upper side of the cathode,bottom curve: current at the bottom side of the cathode).

Vertical Metallization Processes

For the vertical metallization a printed circuit board made from FR4material is used having the dimensions 18″×24″=457 mm×610 mm and athrough-hole diameter of 150 μm and a height of 200 μm.

Before metallization the surface of the printed circuit board is atfirst cleansed for 3 minutes with an acid cleaner S of AtotechDeutschland GmbH and then treated for 60 seconds with 5% sulphuric acid.

The electrolytes used have the following composition. The concentrationof copper ions and sulfuric acid is individually given in the tests. Inall cases, the metallization is carried out at a temperature of 23° C.

-   -   copper sulfate    -   sulfuric acid    -   chloride ions: 60 mg/l in the first step, 35 mg/l in the second.    -   leveling agent Cuprapulse® XP7: 20 ml/l; brightening agent        Cuprapulse® S3:1 ml/l    -   leveling agent Inplate™ DI: 15 ml/l; brightening agent Inplate™    -   DI: 0.5 ml/l    -   Cuprapulse® and Inplate™ leveling agent and brightening agent        are products of Atotech Deutschland GmbH.    -   A redox system is only used in the second step with the        following composition:    -   iron(II): 5 g/l    -   iron(III): 1 g/l

EXAMPLE 5

According to the above-described general execution rule for verticalprocesses the printed circuit board is at first treated for 90 minutesin a bath for electrolytic metallization with copper with theCuprapulse® XP7 process and a pulse reverse current process with theparameters according to Table 5a. Then, in a second step, the printedcircuit board is treated for a further 85 minutes in a bath forelectrolytic metallization with copper with the Inplate™ DI process anda direct current with the parameters according to Table 5b. Then, thefilling of the through-holes is complete. No inclusions are observed.

TABLE 5 pulse parameters in the metallization with copper I_(forward)/pulse parameter pulse phase sulfuric I_(reverse) in ms forward/ pauseshift copper acid test in A/dm² reverse pulse in ms in ° g/l g/l 5a 2/820/1 — 0 17 260 5b 1.5 DC DC — — 40 140

EXAMPLE 6

According to the above-described general execution rule for verticalprocesses the printed circuit board is at first treated for 90 minutesin a bath for electrolytic metallization with copper with theCuprapulse® XP7 process and a pulse reverse current process with theparameters according to Table 6a. Then, in a second step, the printedcircuit board is treated for a further 85 minutes in a bath forelectrolytic metallization with copper with the Inplate™ DI process anda direct current with the parameters according to Table 6b. Then, thefilling of the through-holes is complete. No inclusions are observed.

TABLE 6 pulse parameters in the metallization with copper I_(forward)/pulse parameter pulse phase sulfuric I_(reverse) in ms forward/ pauseshift copper acid test in A/dm² reverse pulse in ms in ° g/l g/l 6a 2/840/2 — 0 17 260 6b 1.5 DC DC — — 40 140

EXAMPLE 7

According to the above-described general execution rule for verticalprocesses the printed circuit board is at first treated for 90 minutesin a bath for electrolytic metallization with copper with theCuprapulse® XP7 process and a pulse reverse current process with theparameters according to Table 7a. Then, in a second step, the printedcircuit board is treated for a further 85 minutes in a bath forelectrolytic metallization with copper with the lnplate™ DI process anda direct current with the parameters according to Table 7b. Then, thefilling of the through-holes is complete. No inclusions are observed.

TABLE 7 pulse parameters in the metallization with copper I_(forward)/pulse parameter pulse phase sulfuric I_(reverse) in ms forward/ pauseshift copper acid test in A/dm² reverse pulse in ms in ° g/l g/l 7a1.5/6 20/1 — 0 17 260 7b 1.5 DC DC — — 40 140

The invention claimed is:
 1. Galvanic process for filling through-holesof a workpiece with metals comprising the following steps: (i) bringingin contact the workpiece containing through-holes with ametal-deposition electrolyte and applying a voltage between theworkpiece and at least one anode so that a current flow is supplied tothe workpiece, wherein the current flow is chosen such that a depositionoccurs in the center of the through-holes and, consequently, thethrough-holes completely or almost completely grow together; (ii)further bringing in contact the workpiece with a metal-depositionelectrolyte and applying a voltage between the workpiece and at leastone anode so that a current flow is supplied to the workpiece, whereinthe through-holes obtained in step (i), which are divided into to halvesare filled by the metal, wherein the current flow in accordance withstep (i) is a pulse reverse current and in every cycle of the current atleast one forward current pulse and at least one reverse current pulseoccurs and that the current flow in accordance with step (ii) is eithera pulse reverse current, a direct current or an alternating current, andwherein the ratio of the duration of the at least one forward currentpulse to the duration of the at least one reverse current pulse isadjusted to 5-75.
 2. Process according to claim 1, characterized in thatthe metallization steps (i) and (ii) are carried out in differentelectrolytes.
 3. Process according to claim 1, characterized in thatmetallization steps (i) and (ii) are carried out in the sameelectrolyte.
 4. Process according to claim 1, characterized in that theduration of the at least one forward current pulse is adjusted to 5-250ms.
 5. Process according to claim 1, characterized in that the durationof the at least one reverse current pulse is adjusted to 20 ms at most.6. Process according to claim 1, characterized in that the peak currentdensity of the at least one forward current pulse at the workpiece isadjusted to 15 A/dm² at most.
 7. Process according to claim 1,characterized in that the peak current density of the at least onereverse current pulse at the workpiece is adjusted to 60 A/dm² at most.8. Process according to claim 1, characterized in that a first voltageis applied between a first side of the workpiece and at least a firstanode so that a first pulse reverse current is supplied to the firstside of the workpiece, wherein in every cycle of this first pulsereverse current at least a first forward current pulse and at least afirst reverse current pulse flow, and a second voltage is appliedbetween a second side of the workpiece and at least a second anode sothat a second pulse reverse current is supplied to the second side ofthe workpiece, wherein in every cycle of this second pulse reversecurrent at least a second forward current pulse and at least a secondreverse current pulse flow.
 9. Process according to claim 8,characterized in that the first current pulses are offset relative tothe second current pulses by about 180°.
 10. Process according to claim1, characterized in that an acid copper electrolyte is used aselectrolyte.
 11. Process according to claim 1, characterized in that theelectrolyte comprises an inorganic matrix comprising 15-75 g/l copper,20-400 g/l sulphuric acid and 20-200 mg/l chloride.
 12. Processaccording to claim 1, characterized in that the electrolyte furthercomprises organic additives selected from brightening agents, levelingagents and wetting agents.
 13. Process according to claim 1,characterized in that the electrolyte is operated with inert anodes witha redox system.
 14. Process according to claim 1, characterized in thatas electrolyte an acid copper electrolyte and as anodes soluble anodesare used.
 15. Process according to claim 1, characterized in that thethrough-holes have a maximum height of 0.05-0.5 mm.
 16. Processaccording to claim 1, characterized in that the through-holes have adiameter of 60 μm-150 μm.
 17. Process according to claim 1,characterized in that the workpiece is board-shaped and hasthrough-holes.
 18. Process according to claim 1, characterized in thatthe workpiece is a printed circuit board or any other board-shapedelectric circuit carrier.
 19. Galvanic process for filling through-holesof a workpiece with metals comprising the following steps: (i) bringingin contact the workpiece containing through-holes with ametal-deposition electrolyte and applying a voltage between theworkpiece and at least one anode so that a current flow is supplied tothe workpiece, wherein the current flow is chosen such that a depositionoccurs in the center of the through-holes and, consequently, thethrough-holes grow together; (ii) further bringing in contact theworkpiece with a metal-deposition electrolyte and applying a voltagebetween the workpiece and at least one anode so that a current flow issupplied to the workpiece, wherein the through-holes obtained in step(i) which are divided into two halves are filled by the metal, whereinthe current flow in accordance with step (i) is a pulse reverse currentand in every cycle of the current at least one forward current pulse andat least one reverse current pulse occurs and that the current flow inaccordance with step (ii) is either a pulse reverse current, a directcurrent or an alternating current, and wherein the ratio of the durationof the at least one forward current pulse to the duration of the atleast one reverse current pulse is adjusted to 5-75, wherein theelectrolyte comprises an inorganic matrix comprising 15-75 g/1 copper,20-400 g/1 sulphuric acid, and 20-200 mg/1 chloride, wherein theelectrolyte comprises organic additives such as brightening agents,leveling agents and wetting agents, and wherein the electrolyte isoperated with inert anodes with a redox system.
 20. Galvanic process forfilling through-holes of a workpieces with metals comprising thefollowing steps: (i) bringing in contact the workpiece containingthrough-holes with a metal-deposition electrolyte and applying a voltagebetween the workpiece and at least one anode so that a current flow issupplied to the workpiece, wherein the current flow is chosen such thata deposition occurs in the center of the through-holes and,consequently, the through-holes grow together; (ii) further bringing incontact the workpiece with a metal-deposition electrolyte and applying avoltage between the workpiece and at least one anode so that a currentflow is supplied to the workpiece, wherein the through-holes obtained instep (i) which are divided into two halves are filled by the metal,wherein the current flow in accordance with step (i) is a pulse reversecurrent and in every cycle of the current at least one forward currentpulse and at least one reverse current pulse occurs and that the currentflow in accordance with step (ii) is either a pulse reverse current, adirect current or an alternating current, and wherein the ratio of theduration of the at least one forward current pulse to the duration ofthe at least one reverse current pulse is adjusted to 5-75, wherein thethrough-holes have a diameter of 60 μm-150 μm. and a maximum height of0.05-0.5 mm, and wherein the workpiece is a printed circuit board or anyother board-shaped electric circuit carrier.